Magnetic compass



Sept. 2, 1941.

K. E. KUNZE ETAL MAGNETIC COMPASS Filed Dec. 17, 1938 FIG. 3

e INVENTORS i atented Sept. 2, i941 STATES PATENT OFFICE MAGNETIC COMPASS Kai-sins E. lKunze, Derry, Pa, and Theodore L.

' Soo-Hoo, Washington, D. G.

Application December 17, 1938, Serial No. 246,440

7 Claims.

The invention relates to damping devices for magnetic compasses.

The major object of the invention is to provide for damping the oscillations of the directive element of a magnetic compass by means independent of motions of the walls of the containing case.

Present-day liquid damped magnetic compasses are, universally, subject to a displacement of the directive element by the damping liquid when the latter is set in rotary motion by the case, during turns. This swirl efiect is unavoidable with the present arrangement wherein the damping liquid is in contact with the walls of the case, which must turn with the ship, as well as with the directive element, which should remain fixed in azimuth.

We are aware that it has been proposed to overcome this inherent defect by limiting the surfaces, with which the damping liquid is in contact, to portions of the directive element, only, but this increases the weight of the directive element to a degree which results in impracticably high values of the pivot pressure.

We combine means for uncoupling the damping liquid from portions of the compass moving with the ship, and means for regulating the pressure on the bearing of the directive element. This combination results in the elimination of the swirl efiect, without impairing the sensitivity of the directive element.

A secondary object of the invention is to decrease the weight of the magnetic compass by decreasing the quantity of damping liquid required.

A third object of the invention is to decrease V the size of the magnetic compas by eliminating the necessity'for the comparatively large spaces between the case and the directive'element, required, at present, to reduce the swirl eiiect to a minimum.

The drawing illustrates several forms of the invention.

Fig. 1 is a center line sectional elevation of a preferred form of the invention, the drawing being the section bb of Fig. 2. v

Fig. 2 is a plan view of the arrangement shown in Fig. 1, the drawing being the section a-a of Fig. 1.

.Fig. 3 is a perspective detail of the lifting magnet shown in Figs. 1 and 2..

Figs. 4 and 5 are views of another form of the invention, Fig. 4 being a center line sectional elevation taken as indicated by 01-11, Fig. 5, while 55 edges of pieces 9 and Fig. 5 is a plan view sectioned as indicated by 0-0, Fig. 4.

Inour present preferred form, the containing case, indicated by the fragments I, Figs. 1 and 2, houses a directive element which is carried by the pivot 2, resting upon a jewel 3 in the conventional manner. A post 4, screwed into a threaded recess in a boss at the bottom of case I, as shown, carries the jewel 3. The pivot is pressed into a'central hole in a disk 5 and the disk is pressed into the upper opening of the funnel-shaped piece it, the disk 5 and piece 6 thereby acting as a frame upon which the directive element is mounted. The framework is completed by the two pieces 1 and 8, which are shaped as portions of spherical shells and which are fastened, concentrically relative to the pivot point, upon the lower flared skirt of the piece 6, as may be seen in Fig. 1. Pieces 9, H), II, and I2, having the shapes of portions of spherical surfaces, together with piece l3 and the lower skirt of piece 6, form a container having the shape of a portion of a spherical shell whose center is at the point of the pivot 2. This container is partially filled with a damping liquid l4. Piece 9 fits, as an inverted cap, over shell 1 and is fastened thereto. Shell it! conforms to the inside surface of piece 8 and is secured to the latter. The lower edges of pieces H and I2 are soldered, respectively, to the upper H). The lower portions of shells II and I2 are also secured, respectively, to the upper portions of pieces 1 and 8. Piece is, shaped in the form of the frustrum of a cone, is soldered to the upper edges of shells H and I2. The directive magnet system is comprised of the two short, thick,bar magnets 55 mounted within the liquid container and secured tothe shells 9 and Hi. The north-seeking poles N of the two magnets point in the same direction and the common magnetic axis of the pair of magnets is the line m-m. The magnets i5 are formed of material of high coerciveforce, and the inner shell 9-H is of magnetic material for the purpose of forming a flux path of low permeability between the adjacent poles of the two magnets. Y

The system so far described constitutes a north-seeking directive element mounted for universalmotion about the point of pivot 2. Compass graduations, or other markings for determining azimuth, may be carried by the directive element in any of. the well known Ways.

Oscillations of the system.about the pivot pointare damped by the inertia of the liquid M. The inertia of the liquid mass causes its own oscillations, set up by the oscillations of the directive element, to be out of phase with the latter. Damping of the oscillations of the directive element follows, because of the viscous drag of the liquid upon the inner walls of its container. Azimuth oscillations, i. e., oscillations about the vertical axis 'vv are damped by the entire liquid mass, while oscillations about any horizontal axis are damped by zones of liquid having the axis of oscillation as their axis. 'Since the damping liquid I4 and the case I are not in mutual contact, the liquid is never set into swirling moabsent,

In order to make practicable the use of a damping liquid carried by the directive elementjas.

described, we employ means, other than the pivot,

for carrying the largest portion of. the weight" of the directive element without introducing ad- I ditional bearing friction or torques tending to rotate the directive element about the pivot point. Withoutsuch means for carrying the larger portion of the weight of the directive element, the use of damping liquid carried by the directive element itselfwould be impracticable, due to the excessive weight on the pivot. The adverse results of excessive pivot pressure are wellknown.

In the arrangement illustrated by Figs. 1 and 2, we use two small horse shoe magnets l6 and I1 attached to the directive element,and a shield I8-I9 of magnetic material, fixed relative to the case I. The magnets 16 and [1 are pressed through holes in the disk 5, the poles being uppermost and arranged, astatically, as shown in Fig. 3. The shield, of magnetic material, composed of upper shell l9 fastened to lower shell [8, has an inside spherical surface whose center is located at the point of pivot 2. The shield is secured to a post 26 which is screwed intoa threaded recess in a boss in the top of case I, as shown. A non-magnetic lining 2| is fitted to the inside surface of the shell 19. Theinside surface of the lining 2| is hemispherical and has its center at the normal position of the point of pivot 2, this surface being of such radius that, during normal use, the directive element may oscillate about the pivot point without mechanical interference fromthe lining, but the clearance is, also, small enough so that the magnets l6 and I1 exert the required lift upon the .direc,-

tive element, due to the tractiveforce acting, bee

tween magnets and shield; The shield l8 -I9 includes a sufiiciently large portion of the entire spherical surface of which it is a part, to insure a radially-directed lift line at all times. That is, the line of the resultant force between the magnets and the shield passes through the pivot point for all positions of the directive element, since the magnets never approach the shield rim closelyenough to be appreciably drawn tangentially toward the pole of the shield. r

Theastatic arrangement of the poles of mag nets "and 11,.Fig'. 3, produces, in conjunction with shield |8 I 9, practically no distortion of the earthsfield in'the vicinity'of the directive magnets l5. Any such distortion is further reduced;

by the presence of the shell of magnetic material 9l l, which acts as a short-circuiting path for the external field. .Thus' the directive element receives the required lift without the introduction of torques tendingto deflectit about anyaxis,

or additional friction tending to retarfdfits motion in any way. The lining 2! acts as a spacer,

thereby preventing'the poles of theliftingmag nets [G and I1, fromjadheringio Ltheshield- IQ tion by the case. Thus the swirl effect is 9 a d 30.

' tapped to receive the shanks of these pivots, and

is carried thereby. The ring 3| is drilled on a if the directive element is lifted off the jewel 3 during vertical accelerations.

A second form of the invention is illustrated by Figs. 4 and 5. Here we again show fragments, only, of a case 22, since the particular construction of the case forms no part of this invention. A spindle 21 is carried by two bearings 23 and 24 for rotation about its own axis z-z, which is normally vertical. The bearings are fitted in bosses 25 and 26 of the case. Secured to the spindle, midway between the bearings, is a ring 28, drilled on a diameter to receive the tips of two pivots A'small gimbal ring 3! is drilled and diameter which is perpendicular to the axis of the pivots 29 and 36, to receive the'tips of two pivots 32 and 33, Fig. 5, these pivots being threaded through the bars 34 and35, forming cross members of a frame 36. The center lines of the pivots 29 and 30 are aligned in the axis :r- -x, while the pivots 32 and 33 determine the axis yy. The three axes x, y, and z are mutually perpendicular. V

The hollow, toroidal, container 31 is fastened to, and carried by, frame 36, the axis of the toroid coinciding, usually, with the axis zz. This is the condition illustrated. The outerwall 38 of the container may be a compass card. Two brackets 39 and 40, fastened to the bottom of container 31, hold the directive magnets 4| and 42. A damping liquid 43 partially fills the con tainer 31. l

A system consistingof four hollow, toroidal, containers 44, 45, 46, and 41 is mounted upon the inner rimof container 31. The four containers are interconnected, as a unit, and the hollow interior spaces are open to each other. The system is partially filled with a damping liquid 48. Containers 44 and-45 have the common toroidal axis a:m, while the axis y-y is common to the remaining pair, 46 and 41.

For reducing the otherwise excessive pressures of the spindle 21 upon the lower bearing 23, we provide a magnetic lifting system comprising the magnet 56, having an hollowcenter, which is pressed into position 'over the boss 26, and the disk 49, of magnetic material, secured upon the spin-.

. directive magnets, around the lower bearing, for

the purpose 'of compensatingthe disturbing effects of the lifting m'agnetsystem upon the directive magnets. compensating system consists of themagnet 53', which-is similar to the magnet 56 and of the pole strength required for the compensation, pressed over the lower boss 25; and a disk of magnetic material 5| mounted in thesameposition relative .to magnet 53'that the disk49occupies relative to the magnet'50. However, the disk 5| is mounted upon a non-magnetic spacer 52, which is;fastened to the. magnet 53, the disk and spacer being drilled toiclear the spindle 21, as shown.

The'action of this directive element is as follows:

The. axis y-y is settled in the magnetic'meridiaii' by the directive magnetsfland ,42. 05-? cillations of the directive element about the? atria-61o axis are damped, mainly, by theinteraction between the liquid 43 and the inner walls of the container 31. The damping is due to the phase difference between the motions of the liquid and the container, the inertia of the liquid causing it to lag behind the motion of the container. The viscous drag exerted by the liquid upon the walls of the container is the actual damping force. The motion of the liquid'is caused only by the accompanying reaction, i. e., theviscous drag of the wallsof container 3'1 upon'the liquid. Hence, the liquid is not set into swirling motion by the rotations of the case 22 during turns of the ship. For this reason, the swirl effect is absent. Oscillations of the directive element about the an axis are damped in a similar manner by the drag of liquid 48 upon the inner walls of the containers 3:! and 35, while the relative motions between liquid 48 and the inner walls of containers 46 and 47 affect the damping of oscillations about the y axis. The three sets of containers, i. e. El; Mi, i5; and 46, 47; thus damp oscillations of the directive element about any axis, by damping the components of the oscillations about their own toroidal axes, without introducing the undesirable swirl eifect.

The magnet 5i pulling upon the disk 49, reduces the pressure of spindle 21 upon the important lower bearing 23 to a workable value. The excessive weight of the directive element, as constructed according to Figs. 4 and 5, would cause the aforesaid pressure to be prohibitive, otherwise. The character of the bearings for oscillations about the x and y axes is such that a reduction of pressure upon these bearings is not necessary. Distortion of the earths magnetic field by the lifting system 49-40 is compensated by the system 5i-53. The required reduction in pivot pressure is thus accomplished without the introduction of torques which would deflect the directive element.

From the foregoing it will be apparent that we provide for the damping of the oscillations of a compass directive element through the use of liquid, in a manner which precludes the possibility of the liquid being forced into swirling motion or disturbed in any way by the compass case, in combination with torqueless magnetic means for influencing the pivot pressure.

It should be readily apparent that the amount of damping liquid required, when the damping is carried out as herein described, is much less than for the same compass clamped in the ordinary way.

It should also be apparent that the space between the directive element and the walls of the containing case may be reduced to a very small value, when the damping liquid is arranged as herein described. This results in a reduction in the size of the compass, as compared with the same instrument damped in the customary manner.

We are aware that methods for reducing pivot pressures have previously been resorted to, but we believe that the combination with the carrying of the damping liquid by the directive element is unique, and that it produces a new and useful result. a

The drawing and the description of the specification illustrate particular embodiments of our combination, but we wish it to be understood that the invention is not limited to these specific forms. Any compass directive element having provision for carrying the damping liquid, and arranged in combination with any suitable magnetic means'for ensuring practicable values of the pivot pressure, comes within the scope of our invention. I

We claim:

1. In a magnetic compass, the combination of a case; a directive magnet system; means for supporting said directive magnet system for three degrees of angular freedom, within said case; magnetic means for continuously exerting a lifting force on'said directive magnet system, without inhibiting said angular freedom; and closed containers, fixed 'to said directive magnet system and containing damping liquid, whereby the angular oscillations of said directive magnet system are damped by liquid carried entirely by the aforesaid closed containers.

2. In a magnetic compass, the combination of a case; a directive magnet system; means for suporting' said directive magnet system for threedegre'es of angular freedom, within said case; means for damping oscillations of said directive magnet, s'ystemrand means for continuously exerting a lifting force on said directive magnet system, without inhibiting said angular freedom; the said means for damping oscillations comprising closed containers rigidly fastened to said directive magnet system and containing damping liquid, whereby the damping liquid is in contact only with surfaces moving with the directive magnet element, while the said means for exerting a lifting force comprises magnetic elements fixed to the directive magnet system and to the compass case, and co-operating to oppose the weight of the directive magnet system.

3. In a magnetic compass, the combination of a magnetic directive element; a case for said di- 1 rective element; means for supporting said directive element for three degrees of angular freedom, within said case; a lifting magnet attached to said directive element; a member of magnetic material attached to said case and co-operating with said lifting magnet to exert a torqueless lifting force on said directive element; and means, comprising closed vessels containing damping liquid, attached to said directive element, whereby oscillations of the said directive element are damped by liquid carried entirely by the aforesaid closed containers.

4. In a magnetic compass, the combination of a case; a magnetic directive element Within said case; a bearing for said directive element, allowing universal angular motion of the directive element about a point fixed within the case; magnetic means, comprising elements fixed, respectively, to directive element and case, said elements being arranged to continuously exert a torqueless lift on the directive element; and means, comprising closed vessels containing damping liquid, fastened to said directive element, whereby oscillations of said directive element aredamped by liquid in contact only with surfaces moving with the directive element.

5. In a magnetic compass, a directive element comprising the combination of a double-walled spherical container having an inner wall of magnetic material; a damping liquid within said container, the inertia of said liquid supplying the damping forces for said directive element; short directive magnets, fixed to and in line within the walls of said container; astatic-ally arranged horse shoe magnets attached to said directive element; .a compass card; a pivot; a framework interconnecting the said card, container, magnets, and pivot, substantially as described in connection with Figs. land 2; a bearing for said pivot; a case for housing said directive element and holding said bearing; aspherically shaped shield, of magnetic material, fixed relative to said case and concentric with the point of said pivot, and which causes said horse shoe magnets to lift part of the weight of said directivesystem off of said bearing; and" a nonmagnetic inner lining for said shield; substantiallyas illustrated by Figs. 1 and 2 of the'accompanying drawings; 7

6. In 'a magnetic compass,' the combination of the magnetic directive element; a bearing for same; damping liquid; closed containers for said liquid, attached to said directive element for damping the oscillations of same; magnetic means for maintaining the pressuresupon the bearing of said directive element within practicable limits without introducing torques tending to deflect the directive element, the'said magnetic means comprisingitwo lift elements, viz., a magnet and a spherically shaped shell of magnetic material placed concentrically with respect to the pivot pointor center of rotation of the directive element, one lift element being attached to the directive element of the compass while the other lift element is attached to the compass case; and magnetic means for annulling the effect of the said lift elements upon the earths magnetic field in the vicinity of the directive element.

7. In a magnetic compass, a spherically shaped shell of magnetic material; means for attaching said shell to the case of the compass, concentrically with respect to the pivot point of the compass directive element; a lifting magnet; and means for attaching said lifting magnet to the directive element in a position for movement of the poles of the lifting magnet adjacent to, but at all times at the same distance from, the inner surface of said shell, and whereby the lifting magnet exerts a continuous lift upon the directive element without impeding the motions of the latter.

. KAROLUS E. KUNZE.

THEODORE L. SOD-H0O. 

